The subject matter disclosed herein relates to a turbine. In particular, the subject matter disclosed herein relates to a turbine having an unbolted portion.
A turbine includes a rotor and a casing surrounding the rotor. A fluid, such as gas, air, or liquid, passes through blades of the rotor to drive a shaft of the turbine. The turbine is designed such that during operation, a clearance exists between the casing and blades, or buckets, of the rotor to prevent rubbing of the buckets against the casing. The clearance is maintained as small as possible to prevent fluid from passing around the outside of the buckets. Instead, the fluid is directed at the buckets of the turbine and between the buckets to allow the turbine to function efficiently.
When the turbine is heated and cooled, the components of the turbine, including the casing, expand and contract according to their thermal response characteristics. If the thermal response of the casing is too slow or uneven around the buckets of the rotor, the buckets rub against the casing. In particular, during start-up, before the casing has been heated and expanded sufficiently, the clearance is small, and uneven expansion of the casing results in rubbing of the buckets against the casing. Since the rubbing of the buckets against the casing leads to loss of material from the bucket tips, the rubbing leads to an increase in the clearance between the casing and the bucket tips, deteriorating performance of the turbine.